1. Field of the Invention
The present invention relates to a semiconductor light emitting device, such as a semiconductor laser or a light emitting diode, using a gallium nitride compound semiconductor.
2. Background Art
In recent years, a semiconductor laser using a nitride III-V compound semiconductor such as AlInGaN has been actively researched and developed as a semiconductor laser which can emit a light in a region, from a blue region to an ultraviolet region, which is required for high density promotion in an optical disc. Thus, the semiconductor laser using the nitride III-V compound semiconductor has already been put to practical use. The semiconductor laser using the nitride III-V compound semiconductor (see, for example, Japanese Patent Laid-Open No. 2002-246642).
In each of the semiconductor lasers, using the nitride III-V compound semiconductors, which have been reported to date, in order that electrons may overflow from an active layer into a p-type cladding layer side to reduce a luminance efficiency, an electron barrier layer is inserted into a side closer to a p-side electrode than to the active layer. Here, the electron barrier layer has a larger band gap than that of the active layer, and has a function of suppressing the overflow of the electrons.
AlGaN or AlInGaN is used as a material for the electron barrier layer. This material has the large band gap as an Al composition ratio thereof becomes larger. In principle, this material becomes the large barrier against the electrons, and thus has the large effect of suppressing the overflow of the electrons. However, when the Al composition ratio of AlGaN or AlInGaN having a small lattice constant becomes large, the crystalline becomes poor, so that crystal defects are generated in the electron barrier layer or in the vicinity thereof. Thus, there is encountered a problem such that the luminance efficiency is actually reduced all the more because of non-radiative recombination due to generation of the crystal defects.
In addition, the electron barrier layer has the larger band gap than that of each of a layer overlying the electron barrier layer and a layer underlying the electron barrier layer. Thus, although the electron barrier layer suppresses the overflow of the electrons, the electron barrier layer impedes injection of holes into the active layer side. In order to reduce this bad influence, the electron barrier layer is normally doped with a p-type impurity. Mg is used as a p-type dopant in the gallium nitride compound semiconductor. However, there is caused a problem such that the luminance efficiency is reduced through light absorption due to Mg as the p-type dopant.